Kevin Johnson recorded data during a brain scan, which uses a technology called functional magnetic resonance imaging at the Medical University of South Carolina.

CHARLESTON, S.C. – Picture this: Your boss is threatening to fire you because he thinks you stole company property. He doesn't believe your denials. Your lawyer suggests you deny it one more time – in a brain scanner that will show you're telling the truth.

Wacky? Science fiction? It might happen this summer.

As you lie flat on your back, a scanner probes the tiniest crevices of your brain and a computer screen asks, “Did you take the watch?”

A South Carolina laboratory, where the scanner is located, reports catching lies with 90 percent accuracy. And an entrepreneur in Massachusetts is hoping to commercialize the system in the coming months.

“I'd use it tomorrow in virtually every criminal and civil case on my desk” to check up on the truthfulness of clients, said attorney Robert Shapiro, best known for defending O.J. Simpson against murder charges.

Shapiro serves as an adviser to entrepreneur Steven Laken and has a financial interest in Cephos Corp., which Laken founded to commercialize the brain-scanning work being done at the Medical University of South Carolina.

The lab isn't alone. Researchers at the University of Pennsylvania recently have reported impressive accuracy through brain scanning. California entrepreneur Joel T. Huizenga plans to use that work to start offering lie-detecting services in Philadelphia this July.

His outfit, No Lie MRI Inc., will serve government agencies and “anybody that wants to demonstrate that they're telling the truth,” Huizenga said.

Both labs use brain-scanning technology called functional magnetic resonance imaging, or fMRI. It's a standard tool for studying the brain, but research into using it to detect lies is still in the early stages. Nobody really knows yet whether it will prove more accurate than polygraphs, which measure blood pressure and breathing rate to look for emotional signals of lying.

But advocates for fMRI say it has the potential to be more accurate, because it zeros in on the source of lying, the brain, rather than using indirect measures. So it may someday provide lawyers with something polygraphs can't: legal evidence of truth-telling that's widely admissible in court. (Courts generally regard polygraph results as unreliable, and either prohibit such evidence or permit it only if both sides in a case agree to let it in.)

Laken said he's aiming to offer the fMRI service for cases of libel, slander and fraud, where it's one person's word against another, and perhaps in employee screening by government agencies. Attorneys suggest it would be more useful in civil than most criminal cases, he said.

Of course, there's no telling where the general approach might lead. A law review article has discussed the legality of using fMRI to interrogate foreigners in U.S. custody. Perhaps police will use it as an interrogation tool, too, or maybe major companies will find it cheaper than litigation or arbitration when an employee is accused of stealing something important, other observers say.

For his part, Shapiro says he'd switch to fMRI from polygraph for screening certain clients, because he says it would be more reliable and maybe more credible to law enforcement agencies.

In any case, the idea of using fMRI to detect lies has started a buzz among scientists, legal experts and ethicists. Many worry about rushing from the lab to real-world use. Some caution that it may not work as well in the real world as the early lab results suggest.

And others worry that it might.

Unlike perusing your mail or tapping your phone, this is “looking inside your brain,” said Hank Greely, a law professor who directs the Stanford Center for Law and the Biosciences.

It “does seem to me to be a significant change in our ability ... to invade what has been the last untouchable sanctuary, the contents of your own mind,” Greely said. “It should make us stop and think to what extent we should allow this to be done.”

But Dr. Mark George, the neurologist and psychiatrist who operates the scanner at the Medical University of South Carolina, said he doesn't see a privacy problem with the technology.

That's because it's impossible to test people without their consent, he said. Subjects have to cooperate so fully – holding the head still, and reading and responding to the questions, for example – that they have to agree to the scan.

“It really doesn't read your mind if you don't want your mind to be read,” George said. “If I were wrongly accused and this were available, I'd want my defense lawyer to help me get this.”

The technology has produced some eyebrow-raising results. George and his colleagues recently reported that by using fMRI data, a computer was able to spot lies in 28 out of 31 volunteers.

The scanner works by bombarding the subject with radio waves and a powerful magnetic field to create detailed images of the brain and detect tiny changes in blood flow in certain areas. Those changes would indicate those areas were working a bit harder than usual, and according to research by George and others, that would in turn indicate the subject was lying.

In a real-world situation, he said, the person being questioned would go through an exercise task as well as being quizzed about the topic at hand. That way, if the computer failed in the experimental task, it would be obvious that it couldn't judge the person's truthfulness.

Because of that, George said, he's comfortable with entrepreneur Laken's plans to introduce the scanning service to lawyers on a limited basis by the middle of this year. Lab studies are obviously necessary, he said, but “at a certain point, you really have to start applying and see how it works. And I think we're getting close.”

But Jennifer Vendemia, a University of South Carolina researcher who studies deception and the brain, said she finds Laken's timetable premature. So little research has been done on using fMRI for this purpose that it's too soon to make any judgment about how useful it could be, she said.

Without studies to see how well the technique works in other labs – a standard procedure in the scientific world – its reliability might be an issue, said Dr. Sean Spence of the University of Sheffield in England, who also studies fMRI for detecting deception.

Speaking more generally, ethical and legal experts said they were wary of quickly using fMRI for spotting lies.

“What's really scary is if we start implementing this before we know how accurate it really is,” Greely said. “People could be sent to jail, people could be sent to the death penalty, people could lose their jobs.”

Greely recently called for pre-marketing approval of lie-detection devices in general, like the federal government carries out for medications.

Judy Illes, director of Stanford's program in neuroethics, also has concerns: Could people, including victims of crimes, be coerced into taking an fMRI test? Could it distinguish accurate memories from muddled ones? Could it detect a person who's being misleading without actually lying?

Her worries multiply if fMRI evidence starts showing up in the courtroom. For one thing, unlike the technical data from a polygraph, it can be used to make brain images that look simple and convincing, belying the complexity of the data behind them, she said.

“You show a jury a picture with a nice red spot, that can have a very strong impact in a very rapid way. . . . We need to understand how juries are going to respond to that information. Will they be open to complex explanations of what the images do and do not mean?”

And there's a philosophical argument in case fMRI works too well.

Greely notes that four Supreme Court justices wrote in 1998 that if polygraphs were reliable enough to use as evidence, they shouldn't be admitted because they would usurp the jury's role of determining the truth. With only four votes, that position doesn't stand as legal precedent, but it's “an interesting straw in the wind” for how fMRI might be received someday, he said.